The present invention relates to the textile industry, in particular to the treatment of yarns by crimping, and relates to a method of crimping yarns. The invention also relates to a device for carrying out this method.
The crimping of textile fibers or yarns using devices generally referred to as stuffer boxes is carried out by a known method. This method consists in directing the yarns to be crimped between two driving rollers that force the yams into a compaction channel. This compaction channel is usually equipped, at the opposite end to the rollers, with a flapper for compacting the yarns inside the stuffer box. The aim of the flapper or similar device is to increase the friction of the fibers or yarns against the walls of the compaction box to the point where the material to be crimped will lose, as it emerges from the driving rollers, its appearance in a longitudinal form and take on an undulating appearance created by the yarns rubbing downstream against the walls of the stuffer box.
The undulation obtained is referred to as primary crimping and this crimping may be very uniform, but if the compaction chamber is of inappropriate volume or geometry, the primary crimping will tend to become secondary crimping which will have the effect of compacting the material differently and, consequently, will tend to make the primary uniform crimping disappear.
In general, stuffer boxes use a thermal fluid, namely steam, to achieve all or part of the crimping. This steam is injected via orifices situated in the walls of the compaction chamber in such a way that the material to be crimped has a tendency to be pushed out of the stuffer box. This results in the need to apply an even more considerable braking force at the outlet of the stuffer box, so the material tends to acquire even more secondary crimping and consequently lose even more primary crimping.
Crimping machines for carrying out such a method are known in particular from FR-A-2 652 359 and U.S. Pat. No. 5,647,109. In these machines, it is impossible to create and maintain the uniform crimping of the fibers or yarns, owing to the fact that the geometry of the compaction box and/or the system of heat treatment cause its destruction.
The object of the present invention is to overcome these drawbacks by proposing a method and a device for crimping yarns which results in perfectly uniform crimping, without the formation of secondary or parasitic crimping.
For this purpose, the method of crimping yarns includes the steps of making the yarns pass through an initial compaction zone of a stuffer box to obtain uniform crimping, then, in a second zone, in causing pre-setting of the resultant uniform crimping as well as guidance of the yarn to the outlet of the stuffer box by means of a pre-setting fluid.
The invention also relates to a device for carrying out this method, in the form of a stuffer box equipped with a compaction chamber comprising driving rollers working in cooperation with doctor blades and a pre-setting and guiding chamber for the crimped yarns, wherein the cross-section of the compaction chamber is adjustable and the pre-setting and guiding chamber has a cross-section greater than that of the sliver of resultant crimped yarns such that one or more spaces are defined around the sliver being related to the delivery means for the pre-setting fluid.